Formation of TCP (2,4,6-trichlorohydroxybenzene)

Open this experiment’s download – and a window – as students prepare a sample of TCP (2,4,6-trichlorohydroxybenzene). Learners will create a reaction between hydroxybenzene (phenol) and chlorine gas, to make the unmistakable compound, and its signature smell. Includes kit list and safety instructions.

This practical should take 20 minutes.

Equipment

Apparatus

• Eye protection
• Clear plastic sheet (eg OHP sheet)
• Plastic Petri dish (eg 5.5 cm diameter)
• Plastic pipette

Chemicals

• Bleach
• Hydrochloric acid, 1 mol dm^–3
• Sodium hydroxide, 1 mol dm^–3
• Hydroxybenzene (phenol)

Health, safety and technical notes

• Students must wear suitable eye protection (Splash resistant goggles to BS EN166 3).
• Hydroxybenzene (phenol) is toxic, corrosive and a mutagen: gloves should be worn (see CLEAPss Hazard HC070a).
• Sodium hydroxide solution, NaOH (aq), 1 mol dm^—3, is corrosive (see CLEAPSS Hazcard HC091a).
• Hydrochloric acid, HCl(aq), 1 mol dm^–3, is low hazard (see CLEAPSS Hazcard HC047a)
• 2,4,6-trichlorohydroxybenzene is harmful if swallowed, irritant to skin, eyes and respiratory system and a probable carcinogen (category 2) – care should be taken to inhale only the smallest amount needed for identification.

Procedure

1. Cover the worksheet with a clear plastic sheet.
2. Place the base of the Petri dish over the circle provided on the worksheet.
3. Cut the end off the plastic pipette and place the small cup – the reaction vessel – at the edge of the Petri dish as indicated.
4. Using the hydroxybenzene (phenol) sampling technique (ask your teacher) place a small quantity of hydroxybenzene (phenol) in the Petri dish as indicated.
5. Add two drops of bleach to the reaction vessel, followed by two drops of hydrochloric acid. Quickly place the lid on the Petri dish.
6. Leave for 15 minutes, then take off the lid. Smell briefly and cautiously – avoid inhaling more than you need. What kind of smell do you recognise?
7. When you have finished, add a few drops of sodium hydroxide to the reaction mixture to dissolve the solid, and then mop up the solution with tissues.

Method

Students cut off the end of the plastic pipette to make a reaction vessel for generating the chlorine gas using bleach and hydrochloric acid.

After about 15 minutes, the lid is taken off the Petri dish and a strong antiseptic smell should be detected.

At the end of the experiment, students add drops of sodium hydroxide solution to the hydroxybenzene (phenol)/TCP residue to dissolve it and then mop up the contents of the Petri dish with a tissue.

Student questions

What do you observe, and can you write equations for the reactions occurring:

1. To produce chlorine?
2. When chlorine reacts with the hydroxybenzene?
3. What type of reaction is this?